The body can naturally produce vitamin D when skin is exposed to sunlight, but this process declines significantly in winter. There also aren't many food sources of vitamin D. But vitamin D is very important to the body.
The vitamin D receptor can be found in many different tissues, and while the vitamin's roles in bone health and calcium level maintenance are well known, less is understood about its other functions, such as how it relates to immunity. Several immune cells have vitamin D receptors and gene activity in those cells can be affected by the vitamin. Low levels of vitamin D have also been associated with a variety of autoimmune disorders including inflammatory bowel disease, multiple sclerosis, psoriasis vulgaris, rheumatoid arthritis, and type 1 diabetes. Studies have also shown that vitamin D supplements can help lower the risk of autoimmune disease.
A new study reported in Science Advances has provided new insights into the link between vitamin D and immunology. This work has shown that vitamin D deficiency in childhood may increase aging in the thymus. The thymus is crucial to immune function, and helps teach immune cells how to differentiate between cells of the self, and foreign invaders that must be eliminated. When immune cells cannot make this important distinction, they may begin to attack the body's own cells and tissues, to cause autoimmune disease.
"An aging thymus leads to a 'leaky' immune system," said senior study author John White, a Professor and Chair at McGill University. "This means the thymus becomes less effective at filtering out immune cells that could mistakenly attack healthy tissues, increasing the risk of autoimmune diseases like type 1 diabetes. Our findings bring new clarity to this connection and could lead to new strategies for preventing autoimmune diseases."
This study used a mouse model, but the researchers are confident that the findings will apply to humans as well because thymus function is very similar in the two organisms.
Previous research has shown that the risk of developing type 1 diabetes in later life was reduced fivefold in children who were given vitamin D supplements in early life. This study was performed in Finland, where long winters leave many people with low vitamin D levels.
In this work, the investigators used a mouse model that was incapable of generating vitamin D. They analyzed tissues in the mice with various methods and found widespread inflammation in these mice, and autoantibodies that targeted pancreatic tissues. Beta cells of the pancreas generate insulin, and when they are lost, type 1 diabetes arises.
A gene expression analysis showed that the thymus of these mice was also aging at an advanced rate. This led to problems with crucial immune cells called T cells, which helps survey the body for foreign invaders, and target them if necessary. Although the thymus of these engineered mice had started out relatively normally, their condition degraded rapidly compared to unaltered mice.
This research highlights the importance of maintaining normal levels of vitamin D, especially in children. The investigators want to learn more about the relationship between the thymus and vitamin D.
Sources: McGill University, Science Advances